Intracellular proteins whose synthesis is triggered after exposure to stress.
Most of the knowledge about this refers to the so-called heat shock proteins. Heat-shock proteins are produced by cells (from bacteria to mammals) immediately after exposure to toxic temperatures (but also other noxious agents).
Plants also produce stress-induced proteins (animal feed, fungal infestation, heat effects) (stress-inducible plant proteins, see PR-10 proteins below), which can also play a role as allergens as "pathogenesis related proteins - PRPs".